Regulator circuit



1948. p. R. GIBBONS ETAL 2,435,961

REGULATOR CIRCUIT Filed May 13, 1944 F IGJ.

INVENTOR. HARRY L. CHANEY DONALD RGIBBONS BY I WJ'M QM.

ATTORNEY Patented Feb. 17, 1948 OFFICE REGULATOR CIRCUIT Donald R.Gibbons, Belmar, and Barry L. Chaney, Red Bank, N. J.

Application May 13, 1944, Serial No. 535,530

(Granted under the act of March 3, 1883, as amended April 30, 1928: 3700. G. 757) 10 Claims.

The invention described herein may be manui'actured and used by or forthe Government for governmental purposes, without the payment to us ofany royalty thereon.

This invention relates to alternating current rectifier circuitsemploying gas-filled grid-controlled rectifier tubes, and moreespecially to the voltage regulation of said circuits.

Grid-controlled thermionic tubes may be broadly grouped into twoclasses, those having uniform control and those having on-oii' control.With uniform control, the current flowing through the plate circuit isat all times under absolute control of the grid, variations in the gridvoltage being accompanied by variations in plate current. Generallyspeaking, only high vacuum tubes are capable of performing this type ofcontrol.

Gas-filled tubes are normally capable of providing only an on-oficontrol, that is, they will permit either the full fiow of currentthrough .the plate circuit or none, but cannot graduate the flow betweenthese limits. Actually, however, this is true only for instantaneousvalues of current and voltage, inasmuch as gas-filled triodes can beused to vary the average flow between zero and maximum in an alternatingcurrent cycle.

Gas-filled tubes find wide application in rectifier circuits since theyare capable of passing comparatively large currents with very littleinternal voltage drop.- The type most commonly employed is the hotcathode mercury vapor tube which, when equipped with a control grid, isknown in the art under various names such as thyratron or grid-glowtube. Gas-filled grid-controlled rectiiier tubes will hereinafter bereferred to in this specification as thyratrons.

In a high-vacuum tube the grid bias may be thought of as adding to orsubtracting from the space charge so that the electrons have more orless difflculty in reaching the plate. There is no discontinuity in thecharacteristic of plate current as controlled by the grid voltage. Inthe thyratron, however, conditions differ greatly between the no-currentand the current passing states. Before sufilcient ionization takes placefor the glow to be established, the tube resembles a high-vacuum tube inthat the space charge prevents the flow of current. If the grid voltageis made less and less negative, nothing occurs until a certain criticalvoltage is attained. Then ionization takes place and the full currentflows limited only by the emission of the oathode and the external loadresistance. There is once the tube has fired, the grid cannot stop theflow of electrons.

There are two general methods of controlling the firing time ofthyratron tubes, an amplitude method and a phase method. In theamplitude case, a direct current voltage applied to the grid is varieduntil the discharge starts, or with a fixed grid voltage the anodevoltage is increased until current flows. The phase method, implies theapplication of alternating current to anode and grid. When the phaserelation between these -A.-C. voltages is such that the grid of a tubeis given the proper critical voltage at some portion of the half-cycleduring which the anode is positive, current will fiow during theremainder of that cycle.

Since the thyratron will pass current in one direction only, it canreadily be used as a rectifier. While the presence of the grid addsnothing to its rectifying properties, it provides a control means forvarying the average output current, this feature serving as the basisfor the present invention.

The output voltage developed by a power sup ply employing thyratronrectifiers is subject to fluctuations arising as a result of A.-C. linevoltage variations, changes in the load impedance imposed upon thesupply, variations in the ambient temperature of the tubes and variousother factors.

Accordingly it is the principal object of this invention toautomatically stabilize the output voltage of power suppliesincorporating thyratron rectifier tubes.

It is a further object of this invention to provide a simple electronicvoltage regulator applicable to thyratron rectifier circuits.

For a better understanding of this invention together with other andiurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing. The scope of theinvention will be pointed out in the accompanying claims.

In the accompanying drawing:

Figure 1 is a characteristic curve of a thyratron rectifier tubeillustrating the influence of the phase relation between grid voltageand plate voltage upon the firing time of the tube,

Figure 2 is a schematic circuit diagram of a. preferred embodiment of myinvention as applied to half wave 'thyratronrectifier power supply.

= cycle, at which V; intersects Eg, in this figure point P. That portionof the Ep curve beginning at a point corresponding with point P and setof! by shading lines represents the conduction period of thyratron. As Visshifted along the horizontal axis so that it falls in and out of phasewith Ep, the position of P, and therefore the average current fiow, iscorrespondingly varied. When the grid and plate voltage are out of phaseno current flows. If the grid voltage is advanced current flows duringpart of the cycle and by advancing the grid voltage until it is in phasewith bleeder resistor 2!. The output of the power sup- I the anodevoltage the current can be made to flow during the entire half cycle.

The phase of Vg' in respect to Ep, and consequently the firing point,may be adjusted in a thyratron circuit by means of conventional phaseshifting networks comprising known combinations of resistance,.capacitance, or inductance.

The firing point may also be adjusted by coming direct current overthealternating current grid voltage, the amplitude of the direct currentbeing a function of the rectifier output of pacitance filter consistingof resistor i9 and condenser 20.. Shunted across condenser 20 is a plyis obtained at the bieeder terminals.

The electronic voltage stabilizer for regulating the output of the powersupply is in the form of adirect current vacuum tube amplifier includinga screen grid tube 22 havinga, source of anode voltage obtained fromdiode rectifier 23. Diode 23 is connected with its plate to the samesecondary winding i3 feeding thyratron l2, while its cathode isconnected to the plate of tetrode 22 through resistor 24. The diode 23output is filtered by a grounded capacitor 26.

The control and screen grid voltages of tetrode 22 are secured from theoutput of the thyratron power supply. The screen grid is connected tothe positive bus 32 through arheostat til, while th control grid isgrounded through resistances 28 and 21. The latter is connected torheostat 30 througha voltage regulator tube 29. The cathode of tetrode22 is connected'to ground through a voltage regulator tube 26 whichserves to maintain the cathode voltage constant.

The plate of tetrode 22 is connected to-the grid circuit of thyratron 82by a conductor iii. Looking at condenser l5, which is in series with theA.-C. grid bias of thyratron i2, it will be seen I that the voltagedeveloped between ground and the anode of tetrode 22 is applied acrosscondenser Id in series opposition with the voltage deanode circuit oftetrode 22 is such that it can the thyratron. Accordingly, variations inthe thyratron output cause corresponding variations in the directcurrent applied to the control grid of said thyratron, thereby alteringthe grid and anode voltages to a degree compensating for the exceed thatacross bleeder 2! so that the resultant D.-C. voltage applied to thegrid of thyratron l2 may be positive or negative with respect to itscathode. Thus the A.-C. component of the grid bias may beshiftedvertically in either direction with respect to its zero axis, asindicated in Fig. 1 by the double headed arrow 42, the shift in thepositive direction being illustrated by a wave Va; v

g The operation of the regulated rectifier circuit is as follows: Thecathode-anode potential for the rectifier is furnished by thesecondaryiii, the circuit being grounded secondary l3, the plate oftriode [2, the cathode of triode i2, resistance l9, condenser 20 toground; in addition to condenser 26 there are three parallel paths whichare: first, resistance 2i second, rheostat 30, regulator. tube 29, andresistance 21, and the third.

A step-up power transformer I0 is provided, 1

juncture of the phase shifting network is connected to the grid ofthyratron i2 through a current limiting resistor It. This RC phaseshift.- ing network is one type of phase-shifting circuit, which may beused to secure the desired phase relation between the plate and gridvoltages.

The wave ripples of the thyratron i2 output are smoothed out by means ofa sedate-noma we tube 29; this potential can be adjusted by vary-- 2shunted with a resistor to prevent the possibility of shock excitedoscillations which are apt to take place because of the relatively steepwave front of the wave appearing in the rectifier out-' put. Resistance2! is a bleeder resistor which shunts condenser 2t and thus provides ashunting path for this filter condenser. The second parallel path whichincludes rheostat 3B, voltage regulator tube 29 and resistance 27,provides the necessary grid potentials for tetrode 22, the screen gridbeing connected to the junction point 'between tube 29 and rheostat 36'.Thus the potential impressed on the screen grid is determined by thevoltage drop across resistance 2-7 and will give proper operation oftetrode 22.

entire circuit including resistance 2?, tube 29,-

ing rheostat 30. Since fairly large fluctuations of the screen gridpotential have a relatively limited effect on the behaviour of tetrode22, it may be assumed that the screen grid potential remains practicallyconstant; this is especially so in view of the regulating action exertedupon the rectifier circuit by tetrode 22. The control grid of tetrode 22is connected through the grid resistor 28 to the junction point betweentube 29 and resistance 21, and therefore the potential of this grid withrespect to the cathode will be determined primarily by the IR dropappearing across resistance 27. The voltage regulator tube 29 isinserted between the resistances 21 and 30 for reducing the positivepotential impressed on the control grid of tetrode 22 to the value thatThe and rheostat to may be considered as a voltage divider with thesignal impressed on the control grid of tetrode 2'2 being determined bythe ratio of the resistance of rheostat 32 to that of resistance 22, theregulator tube 29 merely acting as a device which reduces the positivevoltage impressed on the control grid of tetrode 22 to the desiredextent without further reducing the load voltage fluctuations.-Condenser 36 and resistance 28 comprise a condenser-resistance filterwhich prevents the pronounced ripple appearing in the output of triodel2 to have any eifect on the regulating action of tetrode 22. Thereforethe parameters of this filter must be adjusted so that its time constantis relatively large as compared to the period of the ripple, andrelativeiy short as compared to the voltage fluctuations which are aptto take place because of any changes in the impedance of load 3i and anyvoltage fluctuations across the primary II.

Since resistor 22 is connected in a circuit be-' tween ground and thepositive bus 32, the flow of current through resistance 2'! will manethe control grid of tetrode 22 positive with respect to ground. If thecathode of tetrode 22 were connected directly to ground, tetrode 22would operate on the upper portion of its characteristic because ofpositive grid bias, and since this is an undesirable mode of operationit becomes necessary to raise the potential of the cathode above groundto that point which would enable one to operate tetrode 22 with thegrid'signal with respect to the cathode varying approximately betweenzero grid potential and the cut-off potential. To accomplish this, avoltage regulator tube is connected between ground and the cathode oftetrode 22, the constant voltage drop across this tube raising thepotential of the cathode above ground to establish the above-mentionedmode of operation of this tetrode. It is to be noted that by using avoltage regulator tube rather than a resistance in the cathode circuit,the usual degenerating effect due to the cathode resistance, iseliminated. The anode of tetrode 22 obtains its necessary positivepotential from the secondary winding l3 of transformer id to which it isconnected through diode 23 and resistance 24; this potential is madesubstantially constant by a relatively large condenser 25 consame gridby the phase shifter l5-l1 connected across the secondary H. The gridresistor l8 performs an important function of protecting triode |2against excessive grid currents during the positive excursion of itsgrid during the positive portion of the alternating current waveimpressed upon this grid by the phase shifter. However, the moreimportant function of resistance i8 is to prevent a large flow ofunidirectional current, during the same positive grid excursion, fromthe grid through resistance l8, resistance i'i, secondary i4, conductorMi, junction point 38, resistance 24, diode 23, secondary l 3 to ground,through the grounded resistance 2i, resistance I9 and to the cathode ofthyratron'l2. This path links thyratron i2 to the plateof tetrode 22 atthe junction point 38; the flow ,of such parasitic current through theplate resistor 24-11 allowedwould exert detrimental effect on the normalvoltage regulating function of tetrode 22 by lowering its platepotential. It may be noted here that resistance It may be made very highwithout paralyzing triode i2 since resistance l8 carries no current upto the moment of firing triode i 2; thus, preceding ionization, the gridof triode [2 controls the instant of ionization of triode i2.

The grid of triode i2 is also coupled to its cathode by condenser iii;the function performed by condenser I5 is as follows: if transients orany other disturbances appear in the output circuit of the rectifier,they will be transmitted tothe cathode of triode i2 over bus 32, and ifthere were no condenser i5 in the circuit, these transients would appearonly on the cathode, and the potential of the grid during thesetransients would have been determined solely by the potentials impressedupon it by tetrode 22 and secondary M. Since these potentials would notbe under the influence of the transients, large dif-' ferences ofpotential would be created between the grid and the cathode, and thesewould vary the time of ionization of triode I2. In order to prevent suchdetrimental effect of transients on the operation of triode l2,condenser i5 is inserted between the cathode and the grid whichtransmits all these transients to the grid through condenser IS, thesecondary l4, and resistances I1 and I8, thus raising or lowering thepotential of the grid in synchronism and in phase with the lowering orraising of the cathode potential, which prevents the abnormal firing ofthe triode by the transients.

It may be noted here parenthetically that condenser [5 will alsotransmit the same transients to the plate of tetrode 22. However thiswill have only negligible effect on the normal functioning of tetrode 22because of the protective action exerted by the screen grid of thelatter.

Summarizing the functioning of the rectifier circuit, two alternatingcurrent potentials appear across the secondaries l3 and I4; thealternating current potential appearing across the secondary i3 isimpressed on the anodes of thyratron l2 and tetrode '22, the potentialappearing at the anode of tetrode 22 being a filtered D.-C. potentialnecessary for operation of this tetrode. The alternating currentpotential appearing across the secondary i4 is shifted in phase by thephase shifter Iii-l1, and is impressed on the grid of triode i 2approximately 60 to lagging behind the potential impressed on the plateof this triode. When the grid potential reaches the firing point Pillustrated in Fig. 1, triode l2 becomes conductive and delivers apositive pulse at the cathode of this triode illustrated by the aesaeeiI cross-hatched portion of the voltage wave E3). Thi series of pulses isfiltered by the condenser 26 and resistance or inductance withtheresulathat a suf-iciently constant D.-C. potential appears across theterminals 32 and 3d oi the rectifier. This potential controls the degreeof conductivity of tetrode 22 through the previously described action ofthe potentiometer circuit including resistances 2i and and tube as. Theoutput of tetrode controls the Ill-C. biasing potential impressed on thegrid of triode iii. If the impedance of the load connected across theterminals 32 and 3% is lowered to such an em tent that the voltageappearing across these terminals is lowered, there is a correspondinginstantaneous lowering of the potentials impressed on the control andscreen grids of tetrode 22 with the concomitant lowering of theconductivity of the, latter. It should be noted that the anodeoithis'tetrode is connected to an independent source of positivepotential furnished by the secondary winding it so that any fluctuationin the output circuit of the rectifier does not affect the platepotential of tetrode 22. l'he previously mentioned lowering of theconductivity of tetrode 22 therefore immediately results in the raisingof the potential of the junction point 38, and this rise in potential isat once transmitted through the secondary id and resistances it and it;to the grid of triode This in turn produces the previously mentionedshifting of the. firing point of tetrode it from point P to point P1illustrated in Fig. 1 with the result that triode it becomes conductiveat the earlier portion of the positive cycle of voltage E impressed onthe plate of this trlode. such earlier firing of the triode compensatesthe voltage drop appearing across the rectifier terminals 32 and 35!.due to the decrease in impedance of load 3i with the result that thepotential appearing across these ter-' rninals remains substantiallyconstant irrespective of the fluctuations in the impedance of theconnected load.

The same type of action will take place when there is a fluctuation inthe source of voltage connected to the primary ii, the rise in thisvoltage exhibiting itself as a positive signal on the control and screengrids of tetrode 22, and as an increase in the negative lit-C. signal onthe grid of triode iii. line to the amplification fur-=- nished bytetrode 22 this action will occur in spite of the slight rise in theplate voltages furnished to the tetrode 22 and triode i2.

From the description of the functioning of the rectifier circuit itfollows that the degree of regulation may be controlled by varying thesetting of rheostat til. Moreover, rheostat 3d may be used also forvarying to a very large extent the potential appearing across the ll-C.busses 32-3 3. Thus in one embodiment of the invention the D.-C. voltagewas varied between 500 and 300 volts by varying the setting of rheostatit.

While the invention has been disclosed with a tetrode tube used as theDeC. amplifier 22, equally good results may be obtained with a pentode.A triodc may be also used for accomplishing the sought result but it isnot recommended since triodes would be more affected by any voltagefluctuations appearing at the junction point 3%.

The use or" the term gas-filled triode includes the three element gasdischarge tubes which use gas, or mercury vapor, 'or a mixture of gasesas an ionlzable medium.

While the operation of the electronic stabilizer hereinabove describedhas been illustrated in cornnection with thyratrons of the triode type,it may be applied with equal eaiiectiveness to the multi gridthyratrons. Moreover, the stabilizer circuit is not limited in itsapplication to halt-- wave rectiflers but be employed successfully inassociation with iull w ave and niulti-pltsse rectifier circuits. it isobvicusjoi cciuse, the problem of filtering is greatly simplified -smore rectifier tubes are used.

While there has been described what is at pre ent considered a preferredembodiment of invention, it will be obvious to those s led in the artthat various changes and modifications may be made therein withoutdeparting the invention, and it is, thereiore, aimed in the ep= pendedclaims to cover all such changes and modi= fications as fall within thetrue spirit and scope of the invention.

We claim:

1. In a, regulated power system, the combina= tion comprising a sourceof alternating current, a gas-filled rectifier having a cathode, ananode, and a control electrode, the plate-cathode circuit of saidrectifier being coupled to said source, means for impressing thealternating voltage from said source on said control electrode and saidcathode in displaced phase relationship with re spect to the voltageimpressed on said anode whereby said rectifier normally is fired at apredetermined point on the positive portion of said alternating voltage,a direct-current amplifier having its input circuit connected to andcontrolled only by the output circuit of said rectifier in a, mannerwhereby a regulating voltage is established in the output circuit ofsaid amplifier substantially proportional to the direct component of theoutput voltage of said rectifier, but varying in opposite sense to thevariations of said direct component, means for impressing saidregulating voltage on said control electrode, and a condenserinterconnecting the cathode and the grid of said rectifier for creatinga varying potential difierence between said control electrode and saidcathode equal to the difierence between said regulating voltage and thedirect component of said output voltage, the variation in saiddifference advancing o1 retarding said firing point to a degreesubstantially compensating for fluctuations in said direct component ofsaid output voltage.

2. In a regulated power system, the combination comprising a source ofalternating current, a gasfllled rectifier having a cathode, an anode,and a grid, the plate-cathode circuit of said rectifier being coupled tosaid source. means for impressing the alternating voltage from saidsource on the grid circuit of said rectifier in displaced phaserelationship with respect to the voltage impressed on said plate wherebysaid'rectifier normally is fired at a predetermined point on thepositive portion of said alternating voltage impressed on said plate, a.filter circuit connected to the output of said rectifier, a load circuitconnected to said filter circuit, said filter impressing aunidirectional potential on said lead, a direct current amplifierincluding a vacuum tube having its control means connected only to saidfilter circuit in a manner whereby a regulating direct current voltageis established in the plate circuit of said amplifier, the amplitudevariations of said regulating voltage being greater than and in oppositesense to the corresponding amplitude variations of said unidirectionalpotential, means for impressing said regulating voltage on said controlelectrode, and a condenser interconnecting the cathode and the grid ofsaid rectifier for creating a varying potential difierence between saidcontrol electrode and said cathode equal to the difference between saidregulating voltage and said unidirectional potential, the variation insaid difl'erence advancing or retarding said firing point to a degreesubstantially compensating for fluctuations in said direct component ofsaid output voltage.

3. In a regulated power system, the combination comprising a source ofalternating current, a transformer including a primary and first andsecond secondaries, said primary being connected to said source, arectifier having a cathode, an anode and a control grid, thecathode-anode circuit of said rectifier being connected to said firstsecondary for rectifying the output thereof, a serially connectedresistance-capacitance phase shifting network connected across saidsecond secondary, the Junction point between said capacitance and saidresistance being resistively coupled to the control grid of saidrectifier, a condenser connecting the junction point between saidsecondary and said network to the cathode of said rectifier, whereby thegrid and the plate voltages on said rectifier are in displaced phaserelation, a direct current amplifier including a tetrode having its gridand screen grid elements connected to the output circuit of saidrectifier, whereby a varying control voltage is established in the platecircuit of said amplifier proportional to the output voltage of saidrectifier but having the amplitude variations greater than and inopposite sense to the corresponding amplitude variations in the outputvoltage of said rectifier, and a connection between the plate circuit ofsaid amplifier and said condenser for applying said control voltage tosaid control grid for advancing or retarding said firing point to adegree substantially compensating for fluctuations in said outputvoltage.

4. In a rectifier circuit, a source of alternating current, a directcurrent load circuit, a gasfilled rectifier having a cathode, an anode,and a grid, means for connecting said rectifier between said source andsaid load circuit to-supply said load circuit with rectified voltage andcurrent, means for impressing alternating voltage on said grid from saidsource in lagging relationship with respect to the alternating voltageimpressed by said source on the cathode-anode circuit of said rectifierwhereby said rectifier is rendered con. ductive only during a portion ofthe positive halfcycle impressed on said anode, means connected to andcontrolled by said load circuit, said means impressing a varying directcurrent bias on said grid, having amplitude variations greater than andin opposite sense to the variations of said load voltage and acathode-grid connection for superimposing on the alternating potentialof said grid a potential difference equal to the difierence between saidvarying direct current bias and said rectified voltage, said connectionand said last means maintaining said load voltage substantially constantby varying the tive state of said rectifier cycle.

5. In a regulated power system, a source of alternating current, agas-filled rectifier having a cathode, an anode, and a grid, a directcurrent load circuit, first means for connecting said rectifier betweensaid. source and said circuit to supply said circuit with unidirectionalpotential, second means for impressing alternating voltage on said gridfrom said source in lagging relationship with respect to the alternatingvoltage impressed by said source on the cathodeduring said positivehalfduration of the conduc- U plifier and said load degree of regulationof anode circuit oi. said rectifier, whereby said rectifier is renderedconductive only during a portion of the positive half-cycle impressed onsaid cathode and said anode, a direct current amplifier connected to andcontrolled solely by said load circuit for establishing in the outputcircuit of said amplifier a regulating direct voltage substantiallyproportional to said unidirectional. potential, the amplitude variationsof said regulating voltage being greater than and in onposite sense tothe variations of said unidirectional potential, a connection betweenthe output circuit of said amplifier and said grid for impressing saidregulating direct voltage on the grid of said rectifier whereby thefiring point of said thyratron is advanced or retarded along thepositive portion of the alternating voltage impressed on thecathode-anode circuit of said thyratron to a degree compensating forfluctuations in said unidirectional potential with the variations inimpedance of said load circuit, and a capacitive connection between saidgrid and cathode for transmitting the cathode potential fluctuations tosaid grid.

6. A regulated rectifier circuit including, a source of alternatingcurrent, a direct current load circuit, a gas-filled rectifier having acathode, an anode, and a grid, a transformer having a primary and firstand second secondaries, said prim'ary being connected to said source,said first secondary being connected to the anode-cathode circuit ofsaid rectifier to supply said load circuit with rectified voltage andcurrent, a phase-shifter connected across said second secondary, thegrid of said rectifier being resistively connected to said phaseshifter, a condenser connected between the cathode of said rectifier andsaid second secondary. a direct current amplifier connected to andcontrolled solely by said load circuit, and a connection between theoutput circuit of said amplifier and the junction point between saidsecond secondary and said condenser, said amplifier biasing saidrectifier to maintain said rectified voltage substantially constantirrespective of the fluctuations in the impedance of said load circuitand voltage fluctuations in said source.

7. A rectifier circuit as defined in claim 6 which also includes aunidirectional direct current connection between said first secondaryand the output circuit of said direct current amplifier, said directcurrent connection furnishing the cathode-anode potential for saidamplifier.

8. A rectifier circuit as defined in claim 6 which also includes arheostat in the connection between the input circuit of said directcurrent amcircuit for controlling the said rectified voltage maintainedby said amplifier, and for adjusting the magnitude of said rectifiedvoltage.

9. A rectifier circuit as defined in claim 6 in which the cathode-anodevoltage for said direct current amplifier is ondary whereby thefurnished by said first secconductivity of said direct current amplifieris controlled solely by the voltage fluctuations appearing across saidload circuit.

10. A rectifier circuit as defined in claim 6 in which said directcurrent amplifier includes a series circuit of a grounded resistance, avoltage regulator tube, and a rheostat connected to the positive outputterminal of said rectifier circuit, a multigrid vacuum tube having acathode, an anode, and a plurality of grids, the control grid of saidvacuum tube being connected through a resistance to the junction pointbetween said being connected to the junction point between 2,486,961 a d312 gram e resistance end salcl voltage regulator W4 E tube, and thescreen grid of said vacuum tube R'JERENQES Cm D The following referencesare of record in the said voltage regulator tube and said rheostat, afile this patent! volta e regulator tube between ground and the is UmSTATES PATENTS cathode of said vacuum tube, a. filtering condenserconnected to the control grid of said vacuum tube, Numbe? N Date and aunidirectional direct current connection ,11 Power Apr. 5, 1938 tweenthe enoee oi. said vacuum tube and ai ,1 1 Meyer Mar. 26, 1940 first,secondlg y 2,275,555 Grulhksen Mar. 17, 1942 2,373,759 Faulkner Apr. 17,1945 DONALD R. GIBBGNS.

L. CHANEY.

